When it comes to ecological consciousness in the art world, sculptors lead. Maybe this is because of the claims they make on space and stuff, or perhaps their activity puts them, literally, in touch with environmental realities. This eco-consciousness reflects in two ways: consideration of materials that goes beyond aesthetics, and productions that function as mini-ecosystems.

Three current shows of sculpture prompt thoughts about the fraught relations of man to environment, time to materials, nature to artifice. In Madison Square Park, Roxy Paine has erected stainless steel trees and, in the same material, a boulder. At Galerie Lelong, in Chelsea, veteran land artist Andy Goldsworthy has set in motion an environment that will weather by the day. And Tim Hawkinson, in a pair of exhibitions, tests the capacity of recycled elements to convey the biological condition.

These artists work in different styles and with varying intentions, but each teases audiences with the question: How green is my sculpture?

While Mr. Hawkinson has consistent sculptural interests, he consistently produces what can be called solo group shows, with products so disparate in look, feel, scale, and emotional claim that they could have come from several hands. There are hi-tech things happening in places, such as a quilt constructed through a photorealistic process from a scan of the artist’s foot. There are machines of deliberately intermediate technology (not to count the piece that wasn’t working when I saw it) that take their expressiveness from the clanking, precarious, improvisatory way of amazing machines that only just work. Some works are subtle and thoughtful, others goofy one-liners.

The pervading joke of “How Man Is Knit” seems to be the thought that we are homunculi whose creator is a mad-cap artist like Mr. Hawkinson himself. If Half-Intelligent Design isn’t your theology of choice, you could also take from his work a theory of evolution governed by the survival of the funniest. A sense of man as homemade invention comes across in works — such as “Ranting Mop Head (Synthesized Voice)” (1995), on view at Nyehaus — that have a vintage Dada feel about them.

Mr. Hawkinson’s aesthetic entails a duet of ingenuity and dumbness. “Totem” (2007) is a witty invention in the tradition of Picasso’s sculptures that zoomorphize handlebars or toy cars — here it is plastic jerry cans that do double duty as Easter Island heads. He is protean in such pranks. It is refreshing, in a period of idea-dominated sculpture, to find an artist who reverses the usual ratio: The idea is knowingly banal, but the sculpture comes alive in the making.

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Mr. Goldsworthy is a land artist widely admired beyond the confines of the art world. His popularity was enhanced by a touching documentary film made about him, “Rivers and Tides” (2001), which captured his modus operandi of making impermanent works from found, natural materials in the landscape. He is a hybrid fusion of two culturally distinct forms. On the one hand, he comes out of the earthworks movement of the 1960s, but Mr. Goldsworthy is also strongly rooted in a traditional crafts sensibility.

What we enjoy of Mr. Goldsworthy is secondhand: The main event is (or rather, was) some twig construction lovingly put together in a wilderness and photographed by the artist before being left to the elements. The irony is that this super green sculpture — no waste of resources, no taking up of valuable space, no interference with anyone’s habitat — depends on the virtual, mediated world to be savored. But in his new exhibition at Galerie Lelong, Mr. Goldsworthy has created something whose demise can be witnessed in real time.

Reverting to the minimalist origins of earthworks with a seemingly plain white cube, Mr. Goldsworthy has simply plastered the walls with porcelain clay. You can go there and literally watch the wall dry. In its first days early this week, they were brown from the water-based fixative compound, but as that evaporates the walls will brighten and then begin to crack Mr. Goldsworthy has made such installations before, working with local clays, although in this instance he has used imported moist porcelain from Cornwall, England, where he was born.

While some degree of uncertainty is built into this work — chunks might, after all, fall away from the walls — what seems likely from past precedent is that the walls will dry in a pleasing crackleglaze. The usual balance, in other words, for this artist between craft and conceptualism, cuteness and chance.

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Mr. Paine represents a different side of the same coin as Mr. Goldsworthy. While the British artist makes a fetish out of impermanence and natural substances, Mr. Paine goes to the other extreme, using synthetic materials and advanced technology to simulate processes of decay and erosion.

The work for which he has been best known since the 2002 Whitney Biennial is his series of lifesize stainless steel trees. Three pieces in this genre have been installed for the rest of the year at Madison Square Park. They are, literally, dazzling: Teasing and at the same time nestling in with the real trees, these shiny objects revel in their twin status as aliens and residents. The upper branches of a pair of trees growing into each other, “Conjoined” (2007), look like a lightning field. The boulder piece is “Erratic” (2007), named for the geological phenomenon of objects deposited by glaciers a long way from the materials and processes to which they relate.

Like the boulder, the tree pieces look initially like casts from actual such objects, but are in fact entirely fabricated from existing industrial components. The trees use industrial tubes and pipes, unwieldy materials that Mr. Paine manipulates to his desired shapes using hydraulic bending machines.

While rooted in observation of real trees, Mr. Paine’s species are fictitious, although true, according to the artist, to their own logic. By provoking thoughts about growth versus fabrication, what is natural and what is synthetic, and where the beauty in nature resides, these brilliant things are as green as Mr. Goldsworthy’s twigs.

Hawkinson until June 9 at PaceWildenstein (545 W. 22nd St., between Tenth and Eleventh avenues, 212-989-4258) and until June 16 at Nyehaus (National Arts Club, 15 Gramercy Park South, between Lexington and Park avenues, 212-995-1785);

Goldsworthy until June 16 (528 W. 26th St., between Tenth and Eleventh avenues, 212-315-0470);

Paine until December 31 at Madison Square Park (212-538-4071).