Forest Hills Cemetery is a hilly, 275-acre expanse of shady trees and lawns and paths that wind past graves and memorials ornamented with monuments of every conceivable sort, including weeping marble women, towering stone obelisks, hulking granite lions, and a precious marble girl in a glass gazebo. Designed in 1848 as a welcoming place to have a big picnic and visit one’s Victorian dead while leaving behind the heat and grime of the busy city, it is still a fantastic place to escape to. And it is the final resting place of some wonderful souls. Poets e.e. cummings and Anne Sexton are buried here, along with playwright Eugene O’Neill, abolitionist William Lloyd Garrison, first woman surgeon Susan Dimock, and prominent and obscure Bostonians galore. All now face eternity beneath the hemlocks, spruces, copper beeches, and other fabulous trees — many more than 150 years old — that grace the cemetery.

Last year, the Forest Hills Educational Trust invited artists’ proposals for site-specific work responding to the trees in this unusual setting. The 22 installations selected for exhibition in " Spirits in the Trees " have been executed in materials ranging from recycled metal cans to gold leaf, and they range in scale from the enormous to the tiny. Yet as I trekked from site to site, I was struck by the unity of the works, which I think points to something pervasive about a 21st-century view of the hereafter. All are respectful of the solemnity of their surroundings: in muted earth tones, with organic forms and shapes, many seem to play down the living artist’s hand in the work, going for a seamless coexistence with the trees that inspire them. There is a focus on the ephemeral in contrast to the permanent, and on transitions and passages in contrast to immutable states. The mystery of death and decay amid bountiful life awes us; we do not see in death a gentle sleep, as the Victorians did, or necessarily an elevation to a higher place. Instead, we see an ultimate oneness with nature — with bugs, roots, shadows, and birds — and a transition into the great unknown.

Work that stands out includes two installations by artists who make poetic use of the idea of death’s journey as a small boat, an image and metaphor found in cultures from Egyptian to Eskimo. In Laura Evans’s Horizon, shellacked brown-paper origami boats are suspended from a crabapple tree, like a small fleet of cradles bobbing on the breeze among the leaves. They are translucent, fragile, and empty — transitory vessels situated above our heads to draw our gaze upward. Caroline Bagenal’s Sky Boats are made of more durable fiberglass and are larger in scale, but they too are ephemeral in feeling, and as you look down on them from a grand stone footbridge, they appear to glide past on a mysterious, invisible river.

Other works evoke flight and floatation. Sara Bressem’s Memento Mori is made up of 10 papery balls hanging from a cluster of sugar maples like a group of wasps’ nests or delicate, weightless soccer balls. Each is constructed from mothlike forms, complete with black lines delineating the patterns on their wings and bodies. Bressem has interspersed these markings with many pairs of all-too-human eyes that look down with an inscrutable gaze.

In Anna Johansson’s Reflective Flock, a group of birds constructed from discarded cans soar near the cemetery’s Bell Tower, their metallic cast creating a visual echo to the tones of the bells. Johansson connects the process of recycling material with the passage from the earthly to the spiritual realm, and she’s one of the few artists in this show to explore explicitly the interaction between the natural and the manmade at Forest Hills, relating this natural environment created by humans to her birds, which are natural forms built from manmade materials.

Light captures the essence of spirituality in Shadows, in which artists Clementine Cummer and Susan Nacco have outlined the long shadows of two oak trees with small white stones. Both the grace and the ominous quality of shadows are apparent in this effective piece, which of course describes the actual shadows of the trees only at particular fleeting moments in time. The white " shadows " dance and flicker in a lively, lovely way, but they also have the poignant feeling of Peter Pan trying to stick his shadow back on with soap — stones, no matter how weighty, cannot make our shadows on earth permanent. Our earthly tracks are also the subject of Debra Weisberg’s Footprints, which are precisely that: concrete footprints set into the earth at the side of a stone pathway and slowly disappearing into the roots of an old hemlock.

Whereas only God can make a tree, art is by definition manmade, and it’s often seen as our bid for immortality. Visual artists and poets have many affinities, and one of my favorite works here makes a literary connection with poet e.e. cummings, the master of the lower case. In his sculpture Doorway to the Infinite Yes, artist Gary Orlinsky creates a tall, rounded wooden door, interpreting the idea of the passageway from the known world into the unknown. Steps to the door are inlaid with slate, on which Orlinsky has handwritten a cummings poem exploring life, death, and nature ( " i thank You God for most this amazing/day " ) in the poet’s signature, deceptively childlike voice. Cheryl Sorg’s Transformations also relates poetry and spirituality: the artist cut and reassembled two copies of poet Anne Sexton’s book of the same name into long, single lines of text, which she then draped and looped around the rising limbs of a paper bark maple, underlining the relationship between the tree and the poet’s material, paper, while also literally intertwining the lines of text with the body of the maple.

THE SPIRIT couldn’t be more different, on the face of it, at the ICA’s " Artists Imagine Architecture, " where sculptures made of plywood, cardboard, plastic drinking straws, and scotch tape are on view alongside works incorporating rainbow-colored slinkies and rubber bands. Yet the purposefully impermanent materials (okay, our drinking straws may outlive us, but they don’t convey the same artistic sense of permanence of, say, bronze or marble), the shaky constructions, the modest scale, and the apparently imprecise craftsmanship of most of the works here express the same mistrust of the monumental and the definitive that you’d find at Forest Hills. " Artists Imagine Architecture " presents work by 19 artists who look at architectural models — the foamcore or cardboard tabletop structures, often surrounded by little fake trees and people, that help us envision large-scale projects — and discover much of interest in the scale, impermanence, reality/unreality, and functionlessness of this curious genre.

Some of my favorite works in this show are the smallest and least immediately eye-catching, like Ian Kiaer’s Smithson Upper Lawn Pavilion, in which a light gray painting hangs above a similarly sized cardboard mat upon which sit a tiny house and a long wall. The relationship between canvas and miniature scenario is both poetic and concrete; they are similar in size and in color, yet their scale is in interesting contrast, and their placement raises questions about the abstract and the specific, the infinite and the infinitesimal.

By contrast, Bodys Isek Kingelez’s Palais d’Ihunga (Chicodi Stars) and Kimbembeke Ihunga — bright, circus-like constructions built atop of what look like overturned desk drawers — create a city complete with paved streets, ornate towers, and brightly embellished public-looking squares, all made from bits of metallic tape, cardboard, discarded plastic safety guards from disposable razors, and the like. These works are based on the artist’s vision for the city where he lives, Kinshasa in the Democratic Republic of Congo. His urge to liven up the banal structures of the modern city seems unironically optimistic — the personal can triumph over the institutional.

Color is also employed to great effect in the two pieces from Isa Genzken’s Fuck the Bauhaus series. These works exude the sheer pleasure of construction while poking fun at the high courts of craftsmanship and modernism. Setting his pieces on tall raw plywood pedestals festooned with strips of red nylon tape and white netting, Genzken refers to the familiar forms of sleek modernist architecture while wreaking havoc with them.

Axel Lieber tackles issues of two-versus-three-dimensionality in " Untitled, " a white cube made from a comic strip with its narrative squares removed. Cartoon characters live in two dimensions; by removing the panels in which they act, Lieber abuts the literary and the literal. Also playing with line and space, Thomas Kiesewetter’s sculpture, likewise " Untitled, " looks as if the artist had either painted and bent thin metal to create a laboriously articulated scribble in space or else had had an athletic wrestling match with strange blue ductwork.

" Artists Imagine Architecture " revisits the earliest pleasure we take in constructing small versions of reality from materials readily available to us: a dollhouse from a shoebox, or a model airplane from balsa wood, where no matter what you do the glue or tape gets dirty. But these artists take our shared experience to another level. With intelligence and skill (intentionally camouflaged), they connect our basic impetus to build with the history of what we have built, and they seek to reorient us, from the ground up, away from the clean lines and thoughts of the theoretical to the messy specifics of humanity.